This invention relates to improving the systems and techniques used for completing wells into deep, hot subterranean reservoirs, such as one which contains a corrosive fluid (such as a gaseous fluid capable of corroding the low alloy steels used in sour gas service) at a pressure above about 15,000 psi, a depth below about 20,000 feet, and a temperature above about 300.degree. F.
Prior proposals for completing wells into such reservoirs and numerous problems which have been encountered in such operations are described in the following publications and the references cited therein: "Producing Mississippi's Deep, High Pressure Sour Gas," T. W. Hamby, L. P. Broussard and D. B. Taylor, Journal of Petroleum Technology, June 1976, page 629; "Corrosion Testing of Highly Alloyed Materials For Deep, Sour Gas Well Environments," M. Watkins and J. B. Greer, Journal of Petroleum Technology, June 1976, page 698; and "A Material For Tubing and Casing Applications in Deep, Sour Gas Wells," J. P. T. Forum, Journal of Petroleum Technology, June 1976, page 705.
The publications indicate that such wells have been completed and corrosive fluids such as highly pressurized sour gas have been produced safely. However, the operations have required specially designed procedures and have involved numerous disadvantages. The conduits and valves and the like devices which confine the high pressures must be designed and constructed with materials, such as low alloy steels, that are arranged to provide enough strength to contain the pressures and yet be below the strength or hardness levels of steels that are susceptible to sulfide stress cracking corrosion at the operating temperature ranges. The publications indicate that although suitable strength and resistance levels have been successfully achieved in steels having a minimum yield strength level of 90 KSI (90,000 psi), significant heat-treating problems are encountered regarding elements having walls thicker than about 0.75 inches. Although certain highly-alloyed super austenitic stainless steel tubular goods are inert to corrosion and have yield strengths in the range of 150 to 250 KSI, the attainment of such strengths often requires a significant amount of cold working and aging. The Multiphase MP35N alloy (available from Standard Press Steel Company) requires a 10 to 55% elongation by cold working and aging; and machines are not currently available for accomplishing this on thick-walled elements. Deep, high pressure, sour gas completion designs which have been successful use no downhole packer between the production casing and tubing strings and require that an inhibitor-containing oil be circulated down through the annulus and into the bottom of the tubing string to continually coat the tubing with a corrosion inhibitor. However, as indicated in the publications, such a circulation may fail to prevent corrosion and may also cause a solids-buildup on the inside and outside of the production tubing string.